In searching a liquid sample for the suspected presence of a specific component, or analyte, it is well known in the art to contact the sample with a liquid containing one or more substances which react with the component, i.e., a biospecific molecule. Detecting a reaction between the component and the biospecific molecule may verify the presence of the suspected component in the sample. It is even possible in some cases to determine the amount of the component present in the sample by measuring the degree of the reaction. The inverse is also true, that is, the absence of a reaction may indicate that the component is not present in the sample.
Diagnostic test devices are routinely used for detecting the presence of a component in a liquid sample. Examples of such tests include immunodiagnostic ELISA assays, RNA and DNA hybridization (gene probe) assays, and microbiological assays. A typical diagnostic test device comprises a receptacle which houses a porous reaction medium, i.e., a medium on or in which a reaction can occur.
In performing an analysis of the liquid sample suspected of containing an analyte, the sample is applied to the reaction medium. In some cases the reaction medium may have been pretreated with the biospecific molecule for that analyte. In other cases it may be added prior to, concurrently, or after application of the sample. To insure complete reaction and enhance the reaction rate, the liquids are drawn through the reaction medium by an absorbent in contact with the reaction medium. The liquids applied to the reaction medium eventually saturate it, come into contact with the surface of the absorbent contacting the medium, and are absorbed into the absorbent.
Conventional diagnostic test devices of the type outlined above have several disadvantages. For example, many conventional diagnostic devices fail to properly vent the receptacle. The materials used as absorbents are porous and initially have air enclosed within the pores. As the liquids are absorbed by the absorbent, air is displaced from the pores. If air is not efficiently vented from the receptacle, the displacement of air from the absorbent will be impaired and the effectiveness of the absorbent will be limited, requiring an unduly large amount of absorbent to absorb the liquids. If the receptacle is completely gas tight, or if during use the receptacle is rendered gas tight, the displacement of air from the absorbent will effectively cease. The absorbent will then fail to absorb the liquids through the reaction medium.
Some conventional devices have provided air venting holes in the receptacle. Unfortunately, these holes not only allow the air to vent but may also allow the liquids to escape from the receptacle. This may be particularly dangerous if the liquid sample or the liquid containing the reactant comprise a contaminated, hazardous, or environmentally harmful substance. Alternatively, some diagnostic test devices have receptacles with air venting holes formed therein which are small enough to allow air to pass without allowing liquids to pass. This design may still fail to vent air because the holes may become blocked by the liquids if the liquids contact the surface in which the holes are formed.
In diagnostic test devices as described above, it is important to provide and maintain good contact between the reaction medium and the absorbent. This insures effective absorption of the liquids through the reaction medium by the absorbent. Good contact also helps in achieving reproducible results by insuring a uniform flow of liquids through the reaction medium.